Treatment of inner surfaces of arcuate tubes



Oct. 20, 1959 R. TETTKE, SR 2,909,007

TREATMENT OF INNER SURFACES OF ARCUATE TUBES Filed April 20, 1956 IN VENTOR.

ROMAN TETTKESR BY TREATMENT on INNER SURFACES on ARCUATE TUBESApplication April 20, 1956, Serial No. 579,611 4. Claims. (Cl. 51-58)This invention relates to treatment of the inner surfaces of arcuatetubes, especially inclinometer tubes, and among its objects are theprovision of improved methods and apparatus for reducing irregularitiesand smoothing the inner surface walls of .such tubes.

Ball type inclinometer tubes comprise a glass tube bent in an arc and aball which rolls therein. Such devices are used in a wide variety ofindicator instruments, such as turn and bank indicators in aircraft,trim indicators on ships, and others.

It is essential in devices having inclinometer tubes, that the interiorsurface of the tube over which the ball rolls be perfectly smooth, sothat a reading taken from the instrument will be an accurate indicationof the attitude of the craft in which the instrument is incorporated.Small lumps, or a slight unevenness in the interior wall surface of thetube cause inaccurate readings. Such defects increase the frictionbetween the rolling ball and the tube; they become more pronounced asangular lags are formed and, as a consequence, are the cause forinaccurate indications.

Defects of this nature are usually formed while the tube is being bent.The heating and bending process to which the tube is subjected, causessmall irregularities in the tube wall. These defects are caused by,among other things, uneven temperatures, or small differences in thetube wall. They alter the effective radius over which the ball rolls andproduce discrepancies in readings indicated by the ball.

The foregoing objects, as well as additional and more specific objectsand advantages of this invention, will appear more fully hereinafterfrom a condsideration of the detailed description which follows, takentogether with the accompanying drawings wherein the invention isillustrated.

Fig. 1 is an elevational view of a fire bent inclinometer tubepreparatory to the lapping operation;

Fig. 2 is a view of the lapping slug;

Fig. 3 shows the inclinometer tube mounted to a rock ing machine; and

Fig. 4 shows the processed tube after the lapping operation.

In the drawings there is shown in Fig. 1 an inclinometer tube 1, formedin the usual manner, as by fire bending over a form to a predeterminedradius. Evidences of irregularities, such as lumps, and otherunevennesses in the interior wall surface of the tube are tested for byobserving the actions of the conventional rolling ball used in suchtubes. irregularities are noted by stopping, slowing down and otherirregular actions of the ball as it is caused to roll from one end ofthe tube to the other.

Assuming evidences of such irregularities to have been found, these arecured by a lapping process. To this end a short slug 2, accurately bentto the radius of the inside of the tube is placed within the tubetogether with a solution of a suitable abrasive material such as silicon2,909,007 Patented Oct. 20, 1959 2 carbide grains or other suitablecompound. Sealing corks 3 are plugged in both ends of the tube. Thelatter is then mounted to a suitable motor driven rocking machine 4. Therocking machine operates to rock the. tube first in one direction andthen in the other, as indicated by 'the' dotted lines in Fig. 3, so asto cause the slug 2 to travel back and forth from one end of the tube 3to the other, the stroke of the rocking machine being properly adjustedto this end. 7

Movement of the slug 2 together with the lapping solution during thisrocking operation causes the high spots and other irregularities on theinner surface of; the tube to be ground down to a desired smoothness.

' The tube is tested from time to time as to the effects of the lappingoperation. This isdone by first removing the slug 2 and-washing out thecontents. The conventional'ball used in such tubes is then inserted andcaused to roll back and forth, itsactions being observed as it rolls.After the lapping operation has proceeded for a short time, high spotspartially ground down in the lapping process are visibly indicated.

The lapping compound used in the final stages of the lapping operationis a finishing compound of a relatively finer grain composition thanthat used in the initial part of the operation. The finishing compoundserves to provide a final highly accurate uniformly smooth curved innersurface to the tube.

The slug 2 may be formed of copper and of a material which is not onlyheavy but is also relatively soft. The lapping compound of siliconcarbide grains has a tendency to adhere to the surface of the copperslug because of the particular qualities thereof, whereby the lappingoperation is materially promoted. The ends of the copper slug arerounded as indicated at 5 and this is desirable as the lapping compoundwill tend to accumulate in the space between the tube and the roundedend surface of the slug. This permits the lapping compound to betterattack the wall of the tube as the copper slug pushes the compound backand forth and weighs upon it during the lapping operation.

After examination has revealed the irregularities in the inner surfaceof the tube to have been removed, the tube is washed out. Theconventional ball 6, which may be formed of tungsten carbide, isinserted in the tube. The ends of the tube are then sealed, as at 7, inthe usual manner, and the conventional expansion reservoir 8 isattached. The customary damping fluid is added and the ball 6 will nowroll smoothly over the lapped inner surface of the tube .1 without theheretofore noted irregular actions. Moreover, the added fiuid by wettingthe lapped surface of the tube 1 renders invisible to the eye of theviewer the lapped surface of the inner wall of the tube and causes theball to become sharply visible through the glass of the tube.

While an embodiment of the invention has been illustrated and describedin detail, it is to be expressly understood that the invention is notlimited thereto. Various changes can be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention, as the same will now be understood by those skilled inthe art; and it is my intent, therefore, to claim the invention not onlyin the form shown and described, but also in all such forms andmodificationsthereof as may reasonably be construed to .be Within thespirit of the invention and the scope of the appended claims.

I claim:

1. The method of grinding down to a smooth surface high spots in aninclinometer tube having a predetermined radius, comprising testing thetube for evidences of high spots, performing a slug of copper to a 3radius accurately conforming to that of the inner wall of the tube forsliding action within the tube, inserting the slug together with alapping-compound solution in the tube, sealing the ends of the tube,rocking the tube back and forth to accordingly slide the slug andlapping solution in the tube.

2. In the method as in claim 1, wherein the slug and lapping compoundsolution are cleaned out of the tube from time to time and the tube istested for evidences of the continued existence of high spots.

3. A method of lapping the inner surface Wall of a curved glass tube,comprising the steps of preforming an elongated copper slug to a radiusaccurately conforming to that of the inner wall of the tube and withrounded ends, inserting the slug together with a lapping compoundsolution including silicon carbide grains in the tube, the siliconcarbide grains tending to adhere to the copper slug and accumulatingbetween the rounded end surface of the slug and the inner surface of thetube, and sliding the copper slug and lapping compound back and forth inthe tube so as to lap the inner surface wall of the tube.

4. In lapping apparatus for lapping down to a smooth finish high spotsin the inner wall surface of an arcuate glass tube having apredetermined radius, a copper slug slidably mounted in the tube andbeing relatively smaller than the length of the tube and preformed to aradius accurately conforming to that of the inner wall of the tube, alapping compound solution in the tube, and the copper slug havingrounded ends to enable accumulations of lapping compound thereunder wheninserted with said compound in said tube.

References Cited in the file of this patent UNITED STATES PATENTS970,987 Chaloux Sept. 20, 1910 2,067,474 Carbonara Jan. 12, 19372,311,756 Jackson Feb. 23, 1943 2,353,586 Reininger July 11, 19442,641,093 Kolodny et a1. June 9, 1953 2,648,179 Manes et a1 Aug. 11,1953 FOREIGN PATENTS 106,942 Sweden Mar. 23, 1943

